Currently, video continues to grow in importance. Video is now used for entertainment, business and educational purposes.
Consumer electronics (CE) devices such as digital video disks (DVDs), video cassette recorders, televisions, etc. are frequently used to record and/or playback video information. While many current CE video devices are analog devices such as VHS VCRs, as the cost of digital media and digital players, such as DVD players, decreases, digital CE devices are likely to replace many of the analog devices presently in use.
Theft of copyrighted information, e.g., commercial videos, is a major problem. In order to discourage the copying of, e.g., analog video cassettes, many video distributors intentionally insert noise, as a “copy protection” scheme, into a synchronization portion of the recorded signal. While this noise normally does not significantly effect the viewing of the original cassette, copying of such cassettes using conventional VCRs tends to produce a copy that contains an annoying amount of flicker. The flicker results from inaccuracies is associated with the copying process through which the noise included in the synchronization signal is much more noticeable in the copy than in the recording being copied.
Such known copy protection schemes tend to work reasonably well with current analog VCRs and television sets because such sets are designed to work with a synchronization signal that is relatively noise-free.
While CE devices are tending towards all digital embodiments, analog interfaces with computer monitors are likely to be favored over digital interfaces for quite some time. Generally, for a digital signal to accurately represent an analog video signal, the sampling rate of the digital signal must be at least twice the highest frequency component of the analog signal being represented. Accordingly, to accurately represent high frequency analog video signals, extremely high sampling rates and digital signal processing rates must be supported.
Because of the high signal processing rates that must be supported by digital monitors to display comparable video signals applied to an analog monitor, analog signal processing circuitry included in display devices has tended to be less expensive to implement than digital circuitry. For this reason, among others, analog video signals have generally been preferred to digital video signals for monitor/computer connections. Analog video signals, e.g., VGA signals, usually include, red (R), green (G), blue (B) color signals, horizontal synchronization (HS) signal, and vertical synchronization (VS) signals. Analog interconnects for such signals, e.g., monitor cables, generally include at least one line for each of the R, G, B, HS, and VS signals and at least one line for monitor plug-and-play (PP) signals. Two PP lines are common. A fifteen pin D connector has become a common connector for connecting analog monitors, e.g., VGA monitors, to computer graphics cards and adapters.
Today, many computer monitors are analog “multi-sync” monitors. Such monitors are designed to automatically synchronize to a plurality of signals of different frequencies. Because such computer monitors are designed to handle synchronization signals of multiple frequencies, they are far more flexible than conventional television sets at handling noise and/or slight frequency affects in synchronization signals. For this reason, conventional analog video copy protection techniques, such as that described above, are generally ineffective when applied to video signals supplied to analog multi-sync computer monitors.
In addition to DVDs, digital high definition televisions are likely to become common in the next few years as digital television broadcasts begin and the price of digital television sets decreases.
In order to reduce the risk of unauthorized copying of copyrighted works, several companies, including Hitachi, Ltd., Sony; Intel, and others have proposed an industry standard for digital consumer electronics devices which involves the use of authentication and key exchange procedures along with data encryption and the use of a digital communication bus which complies with IEEE standard 1394. The bus is sometimes referred to as “1394 Firewire”, The proposed standard, hereinafter referred to as the “5C Standard”, is discussed in the 5C Digital Transmission Content Protection White Paper Revision 1.0, dated Jul. 14, 1998.
The 5C standard includes several features. Four such features are:                (1) Copy control requests—A source device can request a destination device to honor copy control requests including copy-never, copy-free, and copy-once requests.        (2) Use of certificates—A destination device proves its trustworthiness to a source device by presenting a digital certificate, e.g., an authentication key, and using a corresponding private key for communications with the source device. The certificate is issued by a certifying authority that has examined the destination device to determine that it will honor the 5C Standard copy control requests.        (3) A key exchange protocol—The protocol is used by the source and destination devices once the destination device has proved that it is certified to establish a session key (content encryption key) used for encrypting copyrighted information to be exchanged.        (4) Transmission of copyrighted information in encrypted form—Information subject to copy restriction requests is transmitted in encrypted form using the session key.        
In the proposed standard, a central authority is responsible for reviewing and certifying devices as complying with 5C Standard copy control requests.
FIG. 1 illustrates a conventional device 100 for implementing the 5C Standard. Device 100 includes authentication and key exchange subsystem 116, optional system renewal subsystem 114, content cipher subsystem 120, IEEE 1394 bus interface 118, storage device 112 for storing video data to be transmitted as well as received video data, and digital bus 122 which is 1394 compliant.
In this system, authentication messages, system renewal messages, authentication keys, exchange keys and session keys, in addition to encrypted data, are passed between the system i00 and other devices via the bus 122. Interface 118 is responsible for electrically interfacing between bus 122 and system elements, such as authentication and key exchange subsystem 116 content cipher subsystem 120. The authentication and key exchange subsystem 116 receives and exchanges, via bus 122, authentication and key information as well as system renewal messages. The content cipher subsystem 120 is responsible for encrypting video information prior to transmission and decoding received encrypted information using content keys provided by authentication and key exchange system 116, to the cipher subsystem 120.
Storage 112 stores un-encrypted video data, copyright status and system renewal information. The system renewal and copyright status information is provided to authentication and key exchange subsystem 116. The video residing in the storage device 112 is supplied to, or received from, the content cipher subsystem 120 which is responsible for encoding/decoding video information passed over bus 122.
In the conventional device, copy protection status information is included in an initial transmission of data between devices along with authentication information, e.g., authentication keys. Copy protection status information indicates that encrypted data can be copied freely, copied for one generation (copy-one-generation), never copied (copy-never) or is subject to a no more copies constraint (no-more-copies). An authentication key is established during authentication, which occurs at the beginning of each exchange of encrypted information between source and destination devices. The authentication key is used to encrypt an exchange key. The exchange key is used to establish and manage security of copyrighted content streams. A content (session) key is exchanged between source and destination devices in conventional device 100. The content key is used to encrypt/decrypt the content being exchanged. Authentication and key exchange subsystem 116 provides the content key, associated with a particular communication, to content cipher subsystem 120 for use in encoding/decoding the content being transmitted or received.
The 5C Standard was designed primarily for digital CE devices. A housing of such devices can normally be sealed in such a manner as to make access to the inside of the device difficult—particularly since consumers rarely need access to the insides of devices such as television sets and VCRs. Furthermore, an amount of control a consumer can have over the data processing performed by most CE devices can be limited to a set of preselected operations, e.g., play, reverse, stop, etc.
Computer owners are accustomed to having easy access to internal components of their systems for upgrading and component replacement purposes. Accordingly, in most cases it would be unacceptable to seal computer housings in such a manner as to deny the owner easy access to internal components of his(her) computer system. In addition, one strength of a personal computer is that it can run arbitrary programs that can interact at a low-level with computer hardware and an operating system. Practically, this means that if unencrypted bits flow through a computer system, often a process can be crafted to steal, e.g., copy, them.
For this reason, computers generally raise more concerns with regard to potential pirating of copyrighted information than, e.g., televisions and other CE products. Because of the ease with which copyrighted data can be copied by computer systems, it is unlikely that computer systems, e.g., personal computers (PCs), are likely to be certified as devices which implement the 5C Standard copy control requests with sufficient certainty to support issuance to it of a 5C certificate. Without such a certificate, a device will be unable to interact and exchange copyrighted information subject to copy constraints with 5C Standard CE devices. The likely inability for a computer system, as a whole, to be certified as a 5C Standard compliant device poses the threat that, in the future, computer systems will be unable to interface with many CE devices.
Another threat to computer system and CE device interoperability has been created by the film industry. A least one major film studio has threatened to refuse licensing high-resolution video if such video will be transmitted on unencrypted analog interconnects.
If copyright owners maintain such a position, it would preclude computer devices from transmitting HDTV to monitors using unencrypted analog lines. The purpose of this 5C Standard is to secure upcoming high-resolution video formats by making it difficult for individuals to connect recorders into the analog stream between a video player and the monitor. A problem with this standard is that it will increase the costs of monitors and video cards.
Unfortunately, an inability to receive certification for a computer system as 5C compliant would prevent that system from displaying copy retrieved movies and other high definition video content where the video is transmitted to a monitor using conventional unencrypted analog monitor interconnects.
In view of the above discussed threats to computer system/CE device interoperability, a need now exists for methods and apparatus that would allow a computer system, or at least a portion of a computer system, to interface and exchange data with 5C Standard devices subject to copy restrictions. In addition, a need also exists for methods and apparatus of implementing some form of encryption or scrambling of video signals on analog interconnects to address concerns of copyright owners regarding unauthorized copying of analog signals. From a commercial standpoint, it is desirable that any new methods and apparatus be at least somewhat backward compatible and be capable of being implemented at a reasonable cost.